People who don’t get much sleep are more likely than those who do to
develop calcium deposits in their coronary arteries, possibly raising
their risk for heart disease, a new study has found.

The 495 participants in the study filled out sleep questionnaires and
kept a log of their hours in bed. At night they also wore motion-sensing
devices around their wrists that estimate the number of hours of actual
sleep. At the beginning, none of the participants, who were ages 35 to
47, had evidence of coronary artery calcification.

Five years later, 27 percent of those who were sleeping less than five
hours a night on average had developed coronary artery calcification for
the first time, while only 6 percent of those who were sleeping seven
hours or more had developed it. Among those who were sleeping between
five and seven hours a night, 11 percent had developed coronary artery
calcification, the study found.

After accounting for various other causes, the researchers concluded
that one hour more of sleep per night was associated with a 33 percent
decrease in the odds of calcification, comparable to the heart benefit
gained by lowering one’s systolic blood pressure by 17 millimeters of
mercury.

The study was published on Tuesday in the Journal of the American
Medical Association. The data were drawn from the ongoing Coronary
Artery Risk Development In Young Adults study.

Senior author Diane S. Lauderdale cautioned that the new report does not
prove a cause-and-effect relationship between a lack of sleep and heart
disease.

“It’s important to say that this is the first report and this does not
yet prove the association is causal,” said Dr. Lauderdale, an associate
professor of health studies at the University of Chicago Medical Center.
“Until we know what the mechanism is -- that it’s really a direct or a
causal relationship -- there is no point in making recommendations based
on this.”

Although a number of studies have suggested that people who sleep less
are at greater risk of heart disease and death, this is the first
investigation to measure how much its subjects actually are sleeping,
said Dr. Sanjay Patel, assistant professor of medicine at Case Western
Reserve University and expert in sleep medicine. Patients’ own
self-assessments can be very inaccurate, he added.

“It’s possible, for example, that people who are under more stress may
be both sleeping less and at higher risk of heart disease,” Dr. Patel
said. If so, he added,

“If we got those people to sleep more but they still were under a lot of
stress, it wouldn’t change their risk of heart disease.”

Higher education levels are also associated with both a lower risk of
heart disease and a tendency to get more sleep, said Dr. Lauderdale.

But it is also possible that lack of sleep leads to certain changes,
like increasing blood levels of the stress hormone cortisol, which can
raise the risk of coronary artery disease over time, Dr. Lauderdale
said.

Another possible mechanism could be through the effect that sleep has on
average blood pressure levels over a 24-hour period. Blood pressure
usually dips when people are asleep, which could provide health benefits
for those who get more sleep, Dr. Lauderdale suggested.

Copyright 2008 The New York Times Company. Reprinted from The New York
Times, National, of Tuesday, December 23, 2008.